The story. Britain's grid hit two milestones in one week: solar peaked at 15.16 GW — 42% of total generation — while the National Energy System Operator (NESO, which runs Great Britain's electricity transmission network) recorded a 98.8% zero-carbon half-hour and gas falling to just 1.2% of the mix (Pvmagazine). It's a preview of summer days when sunshine, not gas, sets the tone.

The bigger picture. The records are a spring spike against a still gas-heavy backdrop. Across all of 2025, gas supplied 90.91 TWh and solar just 19.32 TWh — meaning gas generated nearly five times more electricity than solar over the year (Ember). On April 27, gas was back to 18.2% of the mix and imports led at 21.7% (UK Carbon Intensity API), showing how quickly the picture shifts when the sun sets. The average carbon intensity — grams of CO2 emitted per kilowatt-hour of electricity — sat at 144 that day, well below the 217 annual figure (Ember, 2025) and roughly a third of the world average of 458 (Ember). The solar resource itself is modest: Britain averages 3.31 kWh/m² of usable sunlight per day (Open-Meteo, 2025), far below sunnier grids, so records depend on capacity scaling rather than weather alone.

The tension. NESO's new flexibility auction asks consumers to soak up surplus midday power, but evenings still lean on gas and imports. Cementing the gains means storing the sunshine, not just celebrating the peaks.